1. Field of the Invention
The present invention relates to a polymerizable compound-containing liquid crystal composition and a liquid crystal display device using the same.
2. Description of the Related Art
PSA (Polymer Sustained Alignment)-type liquid crystal display devices have a structure in which a polymer structure is formed in a cell in order to control the pre-tilt angle of liquid crystal molecules, and have been put into practical use as liquid crystal display devices because of their rapid response and high contrast.
A PSA-type liquid crystal display device is manufactured by injecting a polymerizable composition containing a liquid crystal compound and a polymerizable compound between substrates, and polymerizing the polymerizable compound under a condition where liquid crystal molecules are aligned by applying a voltage, thereby fixing the alignment of the liquid crystal molecules. In the PSA-type liquid crystal display device, impurities and a change in alignment of the liquid crystal molecules (change in pre-tilt angle) are known as causes for image sticking as a display defect.
With respect to image sticking due to a change in pre-tilt angle of the liquid crystal molecules, in a configuration of a display device, a polymer structure is changed when the same pattern is continuously displayed for a long time, resulting in a change in pre-tilt angle. Therefore, a polymerizable compound which forms a polymer having a rigid structure with no change in the polymer structure is required.
In order to prevent image sticking by improving the rigidity of a polymer, it has been investigated to constitute a display device using a polymerizable compound having a structure of 1,4-phenylene group or the like, which contains only a ring structure and a polymerizable functional group (refer to Japanese Unexamined Patent Application Publication No. 2003-307720), or constitute a display device using a polymerizable compound having a biaryl structure (refer to Japanese Unexamined Patent Application Publication No. 2008-116931). However, such polymerizable compounds have low compatibility with liquid crystal compounds and thus, when a liquid crystal composition is prepared, precipitation of the polymerizable compounds occurs, leading to the need for improvement.
Further, the PAS-type liquid crystal display devices are used for liquid crystal televisions and the like and thus are highly required to have rapid response. As a method for improving the response speed, various combinations of liquid crystal compositions and polymerizable compounds (WO2010/084823) are disclosed. However, the PAS-type liquid crystal display devices using these liquid crystal compositions have unsatisfactory response speed, and further reduction in voltage is required. Further, the liquid crystal compositions contain chlorine atom-containing liquid crystal compounds and are thus undesirable because reliability of the liquid crystal compositions may be decreased due to the release of chlorine atoms by UV irradiation for polymerization.
Therefore, it is difficult to satisfy the characteristics required for a polymerizable compound-containing liquid crystal composition, such as the image sticking property of a display device, alignment stability, stability of the liquid crystal composition against precipitation, display characteristics, manufacture efficiency in manufacturing a PAS-type liquid crystal display device, etc., leading to the requirement for further improvement.